GENOMIC STRUCTURE OF MOUSE TBXZ AND DETECTION OF EXPRESSION OF TBXZ IN NORMAL AND MALIGNANCE MELANOPHORE BY RT-PCR

T-boxgenesrepresentarecentlyidentifiedfamilyofhighlyevolutionarilyconservedgenesthatencodeproteinsranginginsizefrom--400to>900aminoacids.[],2]Membersofthisgenefamilyshareamotif200aminoacidswhichintheTgeneproducthas.beenshowntoexhibitsequence-specific,DNA-bindingactivity.1']Chapmanandassociates[4]haveshownthatsixmurineT-boxgenesexhibitoverlappingbutuniquepatternsofexpressionduringembryogenesis,indicatingthatexpressionofthesegeneistemporallyandspatiallyregulated.Thissuggeststhat,similartoPaxge…     

Skin too thin? The developing utility of zebrafish skin (neuro)pharmacology for CNS drug discovery research

Skin coloration can be affected by many genetic, environmental and pharmacological factors. Zebrafish (Danio rerio) are a useful and versatile model organism in biomedical research due to their genetic tractability, physiological homology to mammals, low cost, reproducibility and high throughput. Zebrafish coloration is mediated by chromatophores – the skin color pigment cells largely controlled by endocrine and neural mechanisms. The characteristic darkening of zebrafish skin is caused by the dispersion (and paling – by aggregation) of melanosomes (pigment-containing organelles), which show high homology to mammalian structures. Various pharmacological agents potently affect zebrafish coloration – the phenotype that often accompanies behavioral effects of the drugs, and may be used for drug discovery. Although zebrafish behavior and skin responses are usually not directly related, they share common regulatory (neural, endocrine) mechanisms, and therefore may be assessed in parallel during psychotropic drug screening. For example, some psychoactive drugs can potently affect zebrafish skin coloration. Can we use this knowledge to refine phenotype-driven psychotropic drug discovery? Here, we present current models using zebrafish skin coloration assays, and discuss how these models may be applied to enhance in vivo CNS drug discovery.     

Light modulates the melanophore response to α-MSH in Xenopus laevis: An analysis of the signal transduction crosstalk mechanisms involved

Melanin granule (melanosome) dispersion within Xenopus laevis melanophores is evoked either by light or α-MSH. We have previously demonstrated that the initial biochemical steps of light and α-MSH signaling are distinct, since the increase in cAMP observed in response to α-MSH was not seen after light exposure. cAMP concentrations in response to α-MSH were significantly lower in cells pre-exposed to light as compared to the levels in dark-adapted melanophores. Here we demonstrate the presence of an adenylyl cyclase (AC) in the Xenopus melanophore, similar to the mammalian type IX which is inhibited by Ca²⁺-calmodulin-activated phosphatase. This finding supports the hypothesis that the cyclase could be negatively modulated by a light-promoted Ca²⁺ increase. In fact, the activity of calcineurin PP2B phosphatase was increased by light, which could result in AC IX inhibition, thus decreasing the response to α-MSH. St-Ht31, a disrupting agent of protein kinase A (PKA)-anchoring kinase A protein (AKAP) complex totally blocked the melanosome dispersing response to α-MSH, but did not impair the photo-response in Xenopus melanophores. Sequence comparison of a melanophore AKAP partial clone with GenBank sequences showed that the anchoring protein was a gravin-like adaptor previously sequenced from Xenopus non-pigmentary tissues. Co-immunoprecipitation of Xenopus AKAP and the catalytic subunit of PKA demonstrated that PKA is associated with AKAP and it is released in the presence of α-MSH. We conclude that in X. laevis melanophores, AKAP12 (gravin-like) contains a site for binding the inactive PKA thus compartmentalizing PKA signaling and also possesses binding sites for PKC. Light diminishes α-MSH-induced increase of cAMP by increasing calcineurin (PP2B) activity, which in turn inhibits adenylyl cyclase type IX, and/or by activating PKC, which phosphorylates the gravin-like molecule, thus destabilizing its binding to the cell membrane.